1. Field of the Invention
The present invention is related to the field of nano-capsule structures.
The present invention may find its application in many fields, because of the particular properties of such structures. By way of an example, the invention will find an application in the field of energy production, or also in the field of encapsulation of compounds, irrespective of the latter being solid, liquid or gaseous, including vacuum, i.e. at a pressure lower than the atmospheric pressure.
The invention relates more particularly to a method for obtaining nano-capsule structures capable of permitting the encapsulation of a compound. Thus, these structures can also be referred to as nano-tanks and permit a physical encapsulation of various compounds in the three common states of material: solid, liquid or gaseous. It is also possible to encapsulate vacuum.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Nowadays, the chemical encapsulation of compounds is well known. The methods for chemical encapsulation consist in coating a molecule for the purpose of protecting the latter. The main objective of such methods is to permit a release of the molecule encapsulated in a chemical way, in a particular situation. For example, one may wish to achieve a progressive dissolution of the coating in the gastrointestinal tract, so as to release the active substance it contains.
Thus, from the prior art document WO 2009/039458 is known the encapsulation of microstructures or nanostructures with polymeric gels, more particularly micro-gels. Such structures can namely permit the encapsulation of viruses, whereby the latter can serve as a matrix for the synthesis of nanostructures or microstructures.
From WO 2007/003054 is also known a method for the immobilization of bio-molecules on polymers from natural origin or obtained by chemical synthesis, whereby the latter can be functionalized in the form of nano-particles, in order to permit a bonding of the bio-molecule with the nano-particle. The bonding between bio-molecules and polymer particles, for example the nano-particles, occurs by a chemical reaction that is a cycloaddition. Molecules or therapeutic agents can be encapsulated within particles, so as to namely permit their intravenous delivery.
However, the encapsulation by chemical means has several disadvantages. On the one hand, each type of molecule requires a particular encapsulation; indeed, some molecules are more delicate than other and are likely to be destroyed by the coating solution. Therefore, all molecules cannot be coated by means of chemical encapsulation. On the other hand, this type of encapsulation also has limitations as regards the state of the compound to be encapsulated and the quantity. In particular, the gaseous and liquid compounds cannot be encapsulated by chemical means. In addition, the molecular aggregates can only be encapsulated in the case where the coating solution does not dissolve them. Finally, positioning molecules encapsulated by chemical means on a substrate is particularly difficult, which limits the possible fields of application.
The methods consisting in coating a compound by chemical means have some limitations and are not entirely satisfactory.
From WO 2011/102809 is also known a method for encapsulation by chemical means, which attempts to cope with the above drawbacks, in particular by permitting an encapsulation of liquid, solid, or gaseous compounds.
This document relates to a method for obtaining a plurality of micro-chambers. In a first step of this method, a network of micro-wells is printed by nanoimprinting or electron lithography on a polymer substrate. In a second step, a first layer, also of polymer, is applied on this structured substrate.
This first layer consists in particular of a succession of bi-layers, at least 10, each including two differently charged layers. In other words, each bi-layer includes a layer of anionic polymer and a layer of cationic polymer.
Any compound whatsoever is then charged into the micro-wells, then a sealing layer is applied.
The layer-by-layer deposition onto the substrate occurs by soaking the substrate in the different polymer solutions or by implementing a sputtering technique. Such a technique, referred to as “spray coating” in English, is adapted for the deposition of polymers in liquid phase and consists of a propelling, by means of an airflow, of said polymer dissolved in a solvent.
However, the method described in this document still has a number of drawbacks.
In particular, the techniques for depositing the first layer are inaccurate and the polymeric materials being used are not suitable for obtaining an encapsulating layer of a perfectly controlled thickness, while being extremely thin and particularly resistant; therefore, the method only permits to obtain a matrix of micro-chambers, and no isolated structures, and the so obtained matrix does not permit to release each of the micro-chambers independently from each other, without causing the de-structuring of this polymer layer. It is also observed that, since the substrate as well as the first layer are made of polymeric material, the problem of the separation of the micro-chambers from the substrate arises. In any case, this requires the selection of specific polymers, on the one hand, for the substrate and, on the other hand, for said first layer.
In addition, it is difficult to obtain structures of a very small size, in the range of one nanometer, by the implementation of the process steps described in that document. Indeed, the deposition of the first layer by soaking in a solution, or by another cited technique, does not permit an optimal penetration of said solution into a cavity that would have nanometric dimensions, because of capillary and tension forces existing between the first layer and the substrate.
Now, the obtaining of individualized structures nanometric in size is of a particular interest in many fields of application, and namely in the medical field.
Finally, the method described in that document is cumbersome and time-consuming to be implemented. Indeed, besides the plurality of operations of soaking in various polymer solutions necessary to obtain the product, a sonication of the substrate has to be carried out in order to remove the air bubbles likely to cause the formation of a discontinuous and non-uniform layer during the soaking operations.
The inventors have therefore tried to develop a technique permitting to cope with the drawbacks of the chemical encapsulation techniques, and permitting to obtain nano-capsule structures that can namely result into a physical encapsulation of compounds.
As regards the physical techniques, from the state of the art is namely known a method referred to as “lift off”, which permits to structure a resin generally deposited on a substrate. More particularly, the lift-off consists in printing, in a layer of resin deposited at the surface of a substrate, a reverse pattern by electron or optical lithography. A thin metal layer is then deposited by evaporation, so as to try to cover the remaining resin and the portions of the substrate from which the resin has been removed by lithography. Finally, the remaining resin is removed, for example by dissolution, so as to keep only the metal layer that is into contact with the substrate.
Thus, by proceeding to a lithography step, followed by a metal deposition through evaporation and a lift-off of the resin, it is for example possible to obtain a structuring of gold pads on silicon.
From patent document WO 2007/072247 is also known a particular lift-off method, in which a cap-shaped profile is formed in order to permit to obtain a metal layer having a predetermined lateral shape, at a predetermined position of a surface of a semiconductor material. In the same way as the above-cited technique, it only permits to structure pads on the surface of a layer of substrate.
The techniques presently existing in the field of structuring of surfaces thus permit only to obtain monolithic structures, such as pads, and not hollow structures, including thin walls aimed at permitting the encapsulation of compounds, irrespective of same being liquid, solid, or gaseous.
In addition, the technique of deposition of a metal by evaporation is not fully satisfactory. Indeed, there are difficulties in obtaining a continuous, or isotropic, metal layer on the surface of a resin. Furthermore, the techniques for structuring resin are not entirely suitable, and lead to a perforation of the resin, resulting in additional difficulties in the manufacture of closed structures.